Decrease delay to improve battery life

Arbitrary delays were introduced a while ago to deal with device
specific issues but these delays ended up affecting battery life
significantly. Although removing them completely isn't possible,
they can be reduced to more conservative values.

Test: cover prox. sensor multiple times with multiple durations
Fixes: 110902271
Change-Id: I2731fc7a5414f796e96a6c97959c395b10c32faa